Many types of automotive or industrial machinery require placement of bushings to guide or restrain the movement of tie rods, pins, shafts, or bars. Lacking such guide means, a tie rod or other mechanical linkage could uncontrollably vibrate, damaging itself or other essential machinery. To guide such rods, it is a common practice to surround a rod with a bushing, guide sleeve, or similar means for preventing movement of the rod in undesired directions. Generally, this bushing or guide sleeve is permanently mounted to maintain a predetermined direction with respect to a rigid framework or other portion of an automobile or industrial machinery.
For many applications however, simply surrounding the rod with a bushing or other type of guide sleeve mounted to a frame provides a route for the transfer of vibratory motion from the rod to the framework. To inhibit such transfer of vibrational energy through the bushing, it is possible to damp vibration from the bushing to the framework by interposing an intermediary coupling of a vibration absorbing material between the bushing and a mount for the bushing. Because of its low cost, durability, and shock absorbing ability, a commonly employed vibration absorbing material is rubber. Rubber can be molded under high pressure at moderate temperatures to form an elastic mechanical linkage between a bushing and a bushing mount. Vibratory motion transferred from a rod to the bushing is substantially dissipated (as heat) by the rubber surrounding the bushing, greatly reducing the amount of vibration transferred from the bushing to the bushing mount.
However, those skilled in the art have found that high pressure molding of rubber or other elastomeric materials to form an elastic vibration dissipating linkage between bushings and bushing mounts can be difficult. Because of the high pressures required to form high density rubber that tightly couples the bushing to the bushing mount, the bushing must be constructed to withstand substantial inwardly directed radial pressure without breaching or otherwise collapsing under pressure. One method of constructing such high strength bushings is to cut them from commercially available rolled or extruded steel pipe or tubing. The cylindrical shape of the pipe or tube redistributes radially directed forces, minimizing the chance of collapse or breach of the bushing when the bushing is placed under pressure. Bushings are constructed from cylindrical pipe or tube by cutting a desired length of appropriately sized pipe or tube, and machining the ends of pipe or tube by drilling, stamping or cutting to the desired shape. However, this method of bushing manufacture is not preferred because of the high cost of commercially available steel pipe or tube, the difficulty in machining the pipe ends, and the limited range of materials and sizes in which pipes and tubes can be obtained easily.
Bushings can also be formed from coil steel cut into planar, rectangular steel blanks having edges oriented orthogonal to the plane of the blank. The blank can be formed around a mandrel to join two opposed edges and form a generally tubular bushing having an interior cavity through which rods or shafts can be inserted. However, such bushings often cannot be used in conjunction with a high pressure molded rubber vibration damping linkages. During heat treating, such bushings tend to relieve strain by slightly unrolling. This leaves a gap in the joint between the two opposed edges through which molded rubber, injected under high pressure into the volume between the bushing mount and the bushing, can pass into the interior cavity of the bushing and obstruct later insertion of rods, shafts, or the like into the interior cavity of the bushing.
It is therefore an object of the present invention to provide a low cost bushing suitable for use in guide assemblies for moving or vibrating rods, shafts, or the like.
It is another object of this invention to provide a bushing suitable for use in a vibration damping assembly including a bushing, a bushing mount that supports the bushing, and an elastic coupling material positioned between the bushing and the bushing mount to dissipate vibratory motion of the bushing.
Another object of the invention is to provide a bushing that can be formed from low cost coil steel by joining the edges of a steel blank cut from the coil steel and forming the blank into a tubular bushing that resists opening of the joint upon heat treatment of the bushing.
Yet another object of this invention is to form a vibration damping assembly that includes a bushing formed from low cost coil steel, a bushing mount for supporting the bushing in a desired orientation, and a vibration absorbing material injected under pressure into a volume between the bushing and the bush mounting to couple the bushing to the bushing mount and dissipate vibratory motion.
In accordance with the foregoing objectives, an apparatus used in a vibration damping assembly includes a bushing formed to have a substantially tubular shape with an interior surface defining an inner cavity into which moving rods can be inserted, an exterior surface, and a joint having a first edge in overlapping contact with a second edge to form a contact surface. The joint formed by the contact surface between the first and second edges extends between the exterior surface and the interior surface of the bushing.
Generally, a first portion of the contact surface of the joint extends along a plane directed at a non-perpendicular dihedral angle relative to a plane lying tangent to a line formed by the joint on the exterior surface of the bushing so that the first edge of the joint overlaps the second edge of the joint. In alternative embodiments that can be used in conjunction with the foregoing embodiment, a second portion of the contact surface of the joint is formed to extend along a plane directed parallel to a plane lying tangent to the line formed by the joint on the exterior surface of the bushing. In either of the above embodiments, the contact surface forming the joint overlaps even after expansion or slight unrolling of the steel forming the tube, effectively preventing migration of vibration absorbing material (such as rubber) placed in contact with the exterior surface of said bushing through the joint into the inner cavity of the bushing.
One advantage of the present invention is the ease of forming low cost bushings suitable for use in guide assemblies for moving or vibrating rods, shafts, or the like from planar, rectangular steel blanks cut from strips of coil steel. As compared to bushings formed from tubular piping, which must be modified by expensive machining, drilling, or grinding, steel blanks can be inexpensively altered by punching, stamping, or die cutting before being forming the steel blank into a tubular configuration.
Another advantage of the present invention is that bushings having a minimal tendency to unroll in the course of heat treatment can be produced. Such bushings can be used in applications that require precise tolerances and where the bushing must have an unbroken joint that prevents migration of vibration absorbing material into the interior of the bushing.
Yet another advantage of bushings formed in accordance with this invention is their ability to be used as cost effective bushings in vibration damping assemblies that include a bushing surrounded by rubber or other vibration absorbing material. The rubber, injected at high pressure into a mold containing the bushing, will not migrate through the joint into the interior cavity of the bushing. This allows rods, shafts, or other similar devices to be inserted into the interior cavity of the finished bushing without impediment.